In mammalian cells, apoptosis is triggered when cells encounter cytotoxic stresses, such as nutrient withdrawal or DNA damage. These insults initiate signaling cascades that activate pro-apoptotic BH3-only members of the Bcl-2 family of proteins and cause the release of cytochrome c from the mitochondrial intermembrane space into the cytoplasm (Wang, Genes Dev. 15:2922 (2001)). The release of cytochrome c from mitochondria is a key event that triggers the rapid activation of caspases, the key cellular proteases which ultimately execute cell death (Hengartner, Nature 407:770 (2000)).
During normal development of the nervous system, a period of massive neuronal apoptosis occurs to precisely match neurons to their respective target cells (Oppenheim, Annu. Rev. Neurosci. 14:453 (1991)). However, once appropriate neuronal connections are in place, it is imperative that neurons strictly inhibit their apoptotic program since these cells do not divide, have limited capability for regeneration, and must survive for the lifetime of the organism (Benn et al., Nat. Rev. Neurosci. 5:686 (2004)). Although some changes in apoptotic machinery have been identified during neuronal maturation (Putcha et al., J. Cell Biol. 149:1011 (2000); Wright et al., J. Cell Biol. 179:825 (2007); Walsh et al., J. Neurosci. 24:9638 (2004); Tsui-Pierchala et al., J. Neurosci. 19:8207 (1999)), it is unclear whether other mechanisms exist in mature neurons to strictly disable their apoptotic program.
MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression (Bartel, Cell 116:281 (2004)). While mis-expression of some miRNAs has been linked with apoptosis and cancer (Esquela-Kerscher et al., Nat. Rev. Cancer 6:259 (2006); Kent et al., Oncogene 25:6188 (2006)), very little is known about how miRNAs regulate cell death during normal development.
The present invention addresses previous shortcomings in the art by identifying a regulatory role for miR-29 in the expression of the BH3-only family of genes and control of apoptosis in cells and providing methods for inhibiting apoptosis in cells.